1. Field of the Invention
The present invention relates to copolyimides. In particular, it relates to copolyimides prepared from 4,4'-oxydiphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 3,4'-oxydianiline.
2. Description of the Related Art
High performance polyimides are rapidly finding new uses as matrix resins for composites, moldings and films in addition to their traditional use as adhesives. Since these materials display a number of performance characteristics such as high temperature and solvent resistance, improved flow for better wetting and bonding, high modulus, and chemical and hot water resistance, they are useful for the manufacture of lighter and stronger aircraft and spacecraft structures.
One example of this type of polyimide is that prepared by St. Clair et al. in "Polyimide Molding Powder, Coating, Adhesive and Matrix Resin", U.S. Pat. No. 5,147,966. This particular polyimide, referred to hereafter as LaRC.TM.-IA, exhibits excellent thermooxidative stability and is melt processable at temperatures ranging from 325.degree.-350.degree. C. LaRC.TM.-IA has a melt temperature (Tm) of 295.2.degree. C., an enthalpy of 33.2 J/g and a glass transition temperature (Tg) of 229.6.degree. C. As a result of these properties, this polymer has shown potential use for molded parts, films, tubing, aircraft wiring insulation and as a matrix resin for a composite. Unfortunately, it is not resistant to solvent when subjected to stress.
Tamai et al. (European Patent Application number 91304893.0) also prepared LaRC.TM.-IA along with several other readily processable polyimides and copolyimides. An example of one such copolyimide is that prepared from 3,4'-diaminodiphenyl ether (3,4'-ODA), 4,4'-oxydiphthalic anhydride (ODPA) and pyromellitic dianhydride (PMDA). Some of the polymers prepared by Tamai et al. exhibited excellent processability, good chemical resistance and outstanding transparency in addition to excellent heat resistance. However, none of the polyimides were subjected to solvent under stress. Rather, they were tested as powders.
An object of the present invention is to prepare a copolyimide from a diamine and a dianhydride blend.
Another object of the present invention is to prepare a copolyimide which is resistant to solvent when subjected to stress.
Another object of the present invention is to prepare a copolyimide which has improved adhesive properties.
Another object of the present invention is to prepare a copolyimide which retains a low melt viscosity at 350.degree. C. while increasing the stiffness of the polymer backbone.
Another object of the invention is to prepare composites, films and adhesives from the copolyimide.